If you back up to Google Drive, here's what's backed up:

Google Contacts data
Google Calendar events and settings
Wi-Fi networks and passwords
Wallpapers
Gmail settings
Apps
Display settings (brightness and sleep)
Language and input settings
Date and time
Settings and data for apps not made by Google (varies by app)
Note: Not all apps can back up or restore all settings and data. To find out about an app, learn how to contact its developer.